1. Field of the Invention
The present invention relates generally to agricultural implements and, more specifically, to lift wheel structure for an implement frame.
2. Related Art
Implements such as chisel plows and field cultivators have in the past utilized lift wheels connected to a rockshaft assembly on the main frame. The rockshaft assembly is expensive and bulky and often interferes with placement of the implement tools at the desired location on the frame. As a result of permanently mounted lift assembly components, implement versatility is compromised and the number of available tool spacings is reduced. A large tube is required to avoid excessive tube wind up and adds weight to the rear portion of the implement. A compression link operably connects the rockshaft lift wheels with forward wheels to maintain the implement level over a range of vertically adjusted positions. The compression link must be strong to avoid bending under compressive loads and therefore increases costs and adds more weight towards the rear of the implement. The shift of the center of gravity makes the implement back heavy so the front of the frame lifts, especially if additional tools are supported from the rear of the implement. With many lift wheel configurations, the hydraulic cylinders and supports are located behind the center of gravity of the implement, further increasing rear weight distribution.
The front lift wheel assemblies often include four bar linkages having a top bar connected to the compression link or to a cylinder and a bottom bar which is loaded by the weight of the implement and by any additional down forces caused by the tools being drawn into the soil during field working operations. Both bars have to be relatively heavy to handle the respective loads of the lift cylinder or link and the implement weight. Many of the presently available lift wheel assemblies include connecting linkages and cylinders which are offset a substantial distance above the frame and cause interference problems when outer wing sections are folded over the frame for transport. The linkages on wing sections also can also cause interference problems on implements such as five-section machines where the inner and outer wings on each side are pivoted in close proximity during transport. The wheel linkage structures at the front and rear of an implement often have different configurations, and maintaining the implement level in the fore-and-aft direction with mechanically connected lift wheels has been a continuing problem. Some lift wheel assemblies, including those which move vertically by rocking about a single pivot axis, require a considerable amount of fore-and-aft extending space for their full range of vertical motion and further limit the placement of tools on the implement frame. Implements which include electronically controlled depth adjustment often fail to have a convenient and protected location for a potentiometer or other type of transducers located on or adjacent the lift wheel assembly. Linearizing and maximizing movement of a transducer such as a rotary potentiometer in the field working position of the implement continues to be a problem.
It is therefore an object of the present invention to provide an improved lift wheel structure for an implement. It is another object of the invention to provide such a lift wheel structure which overcomes most or all of the aforementioned problems.
It is a further object of the present invention to provide an improved lift wheel structure for an implement having a reduced profile so that interference problems are reduced. It is another object to provide such a structure which increases tool spacing options.
It is still another object of the present invention to provide a lift wheel structure for an implement having an improved four bar linkage. It is another object to provide such a structure which requires a relatively small fore-and-aft dimension for operation over its entire range of vertically adjusted positions. It is a further object to provide such a structure wherein substantially all the heavy loading of the linkage including lift and support loads is borne by the lower link. It is still another object to provide such a linkage which is supported closely adjacent a frame tube and which includes a curved lower link to provide a wheel accommodation space.
It is a further object to provide an improved lift wheel structure which eliminates rockshafts and which can be easily mounted at different locations on the frame. It is a further object to provide such a structure which provides better implement weight distribution and reduces weight at the rear of the implement. It is another object to provide such a structure which eliminates compression links and permits use of shorter frames.
A lift wheel structure constructed in accordance with the teachings of the present invention includes a module type of configuration which can be mounted at different locations along an implement frame. A four bar linkage including a curved lower link is connected to the frame closely adjacent a first tool-carrying rank. A caster wheel is supported at the forward end of the linkage for castering in an accommodation area defined by the curved lower link. Plates are bolted to the sides of the lower link and extend along sides of an upper link to a connection with a lift cylinder directly above the upper link. The lift cylinder is mounted on a support which has an aft portion connected to the rank rearwardly adjacent the first rank and a forward end connected to a casting which pivotally connects the rear pivots of the four bar linkage to the first rank.
The plates extend upwardly from the connection with the cylinder to a pivotal connection with a tension link which extends in the fore-and-aft direction to a connection with a lift wheel assembly which can be either a four-bar arrangement similar to the lift wheel structure describe above or a conventional single arm arrangement. The link and the cylinder closely overlie the frame to limit interference with other components mounted above the frame and to facilitate compact folding of implement sections. The construction eliminates heavy compression links and provides a level lift. The elimination of the rockshaft and rockshaft weldments greatly improves tool and frame component mounting versatility, and the same lift structure module can be used for different implements.
The four-bar linkage provides good vertical lift characteristics with a minimal amount of fore-and-aft space requirements for reduced frame length, improved residue flow and more versatile tool spacing capabilities. A full floating hitch with level lift characteristics eliminates any need for a separate gauge wheel requiring adjustment each time the depth is adjusted. The majority of the linkage loading including that caused by implement weight and tool suction characteristics and lift cylinder lift loading is borne by the lower link, and therefore the upper link can be of a lighter and less costly construction. By connecting the cylinder to the plates extending upwardly from the lower link, the proper moment arm for the cylinder and the necessary arm length for proper front and rear wheel movement are provided without substantial projection of lift assembly components above the frame. The wheel accommodation space opens in the forward direction of tire rotation so that mud is scraped from the wheel and does not wedge between the wheel and upper portion of the curved link. The rear pivot mounting for the four-bar linkage provides a protected space for the rod connecting the wheel position transducer to the lower link. The transducer rod is connected to the link at a point which is at the top of the arc of travel above the lower link pivot to maximize fore-and-aft linear motion in the field working range of the lift wheel. Without the full floating hitch, the operator would possibly have to have a gauge wheel. If this is the case, the operator would then be required to adjust (manually) the gauge wheel each time he adjusted the depth.
These and other objects, features and advantages of the present invention will become apparent to one skilled in the art upon reading the following detailed description in view of the drawings.